The use of fluid transmissions, in which a fluid is used, and mechanical transmissions, in which a planetary gear set or the like is used, to transfer the rotating torque generated by an engine of, for example, an automobile, to the output axle at the wheel-side is well known. The mechanical transmissions can be broadly classified into two types. The first type uses a gear set and thereby gradually transmits the number of revolutions. The second type continuously transmits the number of revolutions.
The mechanical continuously variable transmission is classified in IPC F16 H (transmission apparatus) 15/00 “transmission apparatus for transmitting or reversing rotation having variable gear ratio by means of friction between rotational members,” which also includes mechanical continuously variable transmissions using the “friction.” Needless to say, since the IPC F16H 15/00 classification is further minutely classified, it is understood that a variety of such mechanical continuously variable transmissions using the friction have been proposed.
Recent developments in mechanical continuously variable transmissions have focused on toroidal Continuously Variable Transmissions (CVT), which are a type of a traction drive. The toroidal CVT was first proposed by Charies W. Hunt in U.S Pat. No. 197,472, which has the following basic characteristics. As shown in FIG. 32, a wheel E (hereinafter also referred to as power roller) that slides on disks B and D, which face each other and the inside surface of these disks is formed into a toroidal, i.e., doughnut-like shape, is disposed and by changing the angle of the wheel E, the sliding contact radius of the wheel E can be changed relative to the disk B and disk D sides. Thus, when the rotating torque of the disk B is transmitted to the disk D, the number of revolutions is changed between the disks B and D.
As described above, the toroidal CVT according to the Hunt patent has a toric (i.e. a toroidal shape, like a doughnut) as the entire configuration of the inner surface of the disks B and D. Hence, mechanical continuously variable transmissions that have a configuration like that of the Hunt patent, have been called as toroidal CVTs.
The toroidal CVT according to the Hunt patent, having the basic structure as shown in FIG. 32, is very simple and would have been suitable in a wide variety of industrial applications. There was some experimentation in the application of toroidal CVTs in the 1920s with the emergence of automobiles and various trial products and sales thereof also were made. However, for various reasons, widespread adoption of the toroidal CVT did not occur.
Since then, a variety of improvements to toroidal CVTs have been made. The configuration of the recent toroidal CVTs is largely classified into “full-toroidal” shown in FIG. 33 and “half-toroidal” shown in FIG. 34.
The characteristics of the full-toroidal CVT are basically the same as the Hunt patent. As shown in FIG. 33, the center (the center of the straight line connecting the contact points O and O′ between the input and output disks) of the power roller (in FIG. 32, equivalent to the wheel E) goes through the center of a toroidal cavity formed by the inner surfaces of the disks. In this arrangement, because the pressure between the disks applied to transmit power between the input and output disks does not act on the support axle for relatively inclining the power rollers, the angle of the power roller can be changed smoothly. From an alternative perspective, because the two tangent lines drawn from each contact points 0 and 0′ are parallel to each other, a large spin arises at the respective contact points.
On the other hand, in a half-toroidal CVT shown in FIG. 34, the two tangent lines from each of the contact points O and O′are not parallel to each other but have an intersection point E. When the intersection point E is on the rotation axle I, the spin at each contact point O, O′ is eliminated, resulting in an effective CVT.
In any case, in a toroidal CVT, high pressure is exerted on the metal components in order to keep the components pressed against each other when they come into contact with each other at the shaded portions in FIG. 35 (TANAKA Hirohisa, “Toroidal CVT” (in Japanese), published in July 2000 by Corona Publishing). When the metals come into contact with each other at such small contact portions, as shown, friction heat is inevitably generated.
If there is no means to dissipate the friction heat, the metal components will eventually seize up on each other. Thus, it is necessary to interpose oil between the contact portions. Further, in the toroidal CVT, it is necessary to press the metal components (disk or roller) with an extremely strong pressure. Accordingly, the pressure of the oil interposed therebetween must also be correspondingly high. Thus, in the case where the toroidal CVT is applied to an automobile, the oil pressure would be increased, for example, by using the power of the engine, which, in turn, reduces, “fuel economy”.
Furthermore, when a conventional CVToperates in “reverse” the speed cannot be shifted. It is desired to develop a continuously variable transmission capable of continuously shifting in any rotational direction i.e. (forward/reverse) from an idling state (neutral).
Accordingly, the inventor of the present invention examined recent toroidal CVTs from various viewpoints to evaluate approaches to solving the above-described problems with continuously variable transmissions. The inventor discovered that when a conventional toroidal CVT is used in an automobile fuel consumption increases because the metal components are in “pinpoint” contact with each other. Thus, leading to the present invention.
That is to say, an object of the present invention is to improve mechanical CVTs by arranging the metal components of the transmission so that the components come into “line contact” with each other rather than the conventional “pinpoint contact”. As a result of the line contact between the components, another object of the present invention is to reduce the pressure exerted between the respective metal components. The reduction in pressure between the components results in a reduction in the extra energy needed to maintain the operation thereof. By reducing the pressure between the metal components, the fuel consumption of automobiles using a mechanical CVT can be reduced.